A portion of the disclosure of this patent document (software listings in Appendices A and B) contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of this patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights and protection whatsoever.
A computer program listing appendix that lists the steps of a computer program that is used in carrying out the present invention is set forth in Appendix A and in Appendix B. The computer program listing in Appendix A and in Appendix B is provided on a Compact Discxe2x80x94Read Only Memory(CD-ROM) in accordance with 37 CFR xc2xa71.52(e). The computer program listing appendix that is set forth in Appendix A and in Appendix B is hereby incorporated by reference in this document for all purposes. A copy of Appendix A and a copy of Appendix B are on CD-ROM Copy 1 and duplicate copies of Appendix A and Appendix B are on CD-ROM Copy 2. Each CD-ROM contains a file entitled xe2x80x9cAppendixCD-ROMxe2x80x9d that is 51 KB in length and that was created on Jun. 17, 2002.
The present invention is directed, in general, to control systems for process facilities and, more specifically, to systems for generating and using lookup tables with process facility control systems and models of the same, and methods of operating such systems, all for use to optimize process facilities.
Presently, process facilities (e.g., a manufacturing plant, a mineral or crude oil refinery, etc.) are managed using distributed control systems. Contemporary control systems include numerous modules tailored to control or monitor various associated processes of the facility. Conventional means link these modules together to produce the distributed nature of the control system. This affords increased performance and a capability to expand or reduce the control system to satisfy changing facility needs.
Process facility management providers, such as Honeywell, Inc., develop control systems that can be tailored to satisfy wide ranges of process requirements (e.g., global, local or otherwise) and facility types (e.g., manufacturing, refining, etc.). A primary objective of such providers is to centralize control of as many processes as possible to improve an overall efficiency of the facility. Each process, or group of associated processes, has certain input (e.g., flow, feed, power, etc.) and output (e.g., temperature, pressure, etc.) characteristics associated with it.
In recent years, model predictive control (xe2x80x9cMPCxe2x80x9d) techniques have been used to optimize certain processes as a function of such characteristics. One technique uses algorithmic representations to estimate characteristic values (represented as parameters, variables, etc.) associated with them that can be used to better control such processes. In recent years, physical, economic and other factors have been incorporated into control systems for these associated processes. Examples of such techniques are described in U.S. Pat. No. 5,351,184 entitled xe2x80x9cMethod of Multivariable Predictive Control Utilizing Range Control;xe2x80x9d U.S. Pat. No. 5,561,599 entitled xe2x80x9cMethod of Incorporating Independent Feedforward Control in a Multivariable Predictive Controller;xe2x80x9d U.S. Pat. No. 5,574,638 entitled xe2x80x9cMethod of Optimal Scaling of Variables in a Multivariable Predictive Controller Utilizing Range Control;xe2x80x9d U.S. Pat. No. 5,572,420 entitled xe2x80x9cMethod of Optimal Controller Design of Multivariable Predictive Control Utilizing Range Controlxe2x80x9d (the xe2x80x9c""420 Patentxe2x80x9d); U.S. patent application Ser. No. 08/850,288 entitled xe2x80x9cSystems and Methods for Globally Optimizing a Process Facility;xe2x80x9d U.S. patent application Ser. No. 08/851,590 entitled xe2x80x9cSystems and Methods Using Bridge Models to Globally Optimize a Process Facility;xe2x80x9d and U.S. patent application Ser. No. 09/137,358 entitled xe2x80x9cControllers that Determine Optimal Tuning Parameters for use in Process Control Systems and Methods of Operating the Same,xe2x80x9d all of which are commonly owned by the assignee of the present invention and incorporated herein above by reference for all purposes.
Generally speaking, one problem is that conventional efforts, when applied to specific processes, tend to be non-cooperative (e.g., non-global, non-facility wide, etc.) and may, and all too often do, detrimentally impact the efficiency of the process facility as a whole. For instance, many MPC techniques control process variables to predetermined set points. Oftentimes the set points are a best estimate of a value of the set point or set points. When a process is being controlled to a set point, the controller may not be able to achieve the best control performances, especially under process/model mismatch.
To further enhance the overall performance of a control system, it is desirable to design a controller that deals explicitly with plant or model uncertainty. The ""420 Patent, for example, teaches methods of designing a controller utilizing range control. The controller is designed to control a xe2x80x9cworst casexe2x80x9d process. An optimal controller for the process is achieved and, if the actual process is not a xe2x80x9cworst case process,xe2x80x9d the performance of the controller is better than anticipated.
There are a number of well known PID xe2x80x9ctuningxe2x80x9d formulas, or techniques, and the most common, or basic, PID algorithm includes three known user specified tuning parameters (K, xcfx841, xcfx842) whose values determine how the controller will behave. These parameters are determined either by trial and error or through approaches that require knowledge of the process. Although many of these approaches, which are commonly algorithms, have provided improved control, PID controller performance tuned by such algorithms usually degrades as process conditions change, requiring a process engineer, or operator, to monitor controller performance. If controller performance deteriorates, the process engineer is required to xe2x80x9cre-tunexe2x80x9d the controller.
Controller performance deteriorates for many reasons, although the most common cause is changing dynamics of the process. Since PID controller performance has been related to the accuracy of the process model chosen, a need exists for PID controllers that allows for such uncertainty by accounting for changing system dynamics. Further, the requirement for ever-higher performance control systems demands that system hardware maximize software performance. Conventional control system architectures are made up of three primary components: (i) a processor, (ii) a system memory and (iii) one or more input/output devices. The processor controls the system memory and the input/output (xe2x80x9cI/Oxe2x80x9d) devices. The system memory stores not only data, but also instructions that the processor is capable of retrieving and executing to cause the control system to perform one or more desired functions. The I/O devices are operative to interact with an operator through a graphical user interface, and with the facility as a whole through a network portal device and a process interface.
Over the years, the quest for ever-increasing process control system speeds has followed different directions. One approach to improve control system performance is to increase the rate of the clock that drives the system hardware. As the clock rate increases, however, the system hardware""s power consumption and temperature also increase. Increased power consumption is expensive and high circuit temperatures may damage the process control system. Further, system hardware clock rate may not increase beyond a threshold physical speed at which signals may be processed. More simply stated, there is a practical maximum to the clock rate that is acceptable to conventional system hardware.
An alternate approach to improve process control system performance is to increase the number of instructions executed per clock cycle by the system processor (xe2x80x9cprocessor throughputxe2x80x9d). One technique for increasing processor throughput calls for the processor to be divided into separate processing stages. Instructions are processed in an xe2x80x9cassembly linexe2x80x9d fashion in the processing stages. Each processing stage is optimized to perform a particular processing function, thereby causing the processor as a whole to become faster. There is again a practical maximum to the clock rate that is acceptable to conventional system hardware.
Since there are discernable physical limitations to which conventional system hardware may be utilized, a need exists broadly for an approach that decreases the number of instructions required to preform the functions of the process control system. A need exists for such an approach that accounts for process uncertainty by accounting for changing process dynamics.
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide systems and methods of operating such systems for populating and using lookup tables with process facility control systems, as well as models of the same. In accordance with an exemplary embodiment below-discussed, the principles of the present invention may be used to define and populate a lookup table in response to the needs of a global controller. The lookup table is populated with a range of possible values of at least one measurable characteristic associated with one or more processes of the process facility and in accordance with a model of at least a portion of the same.
Rather than calculate and re-calculate certain characteristics associated with a process or process model, which would consume significant system resources, the present invention introduces a data structure capable of maintaining a range of possible values of one or more of such certain characteristics. Use of the lookup table in lieu of execution and re-execution of the instructions for performing characteristic calculations decreases the number of instructions required to preform the functions of the process control system. The lookup table, once suitably populated, accounts for process uncertainty by maintaining the range of possible values, thereby accounting for changing process dynamics.
An exemplary computer system for use with a process facility that is capable of populating a data structure in accordance with the principles of the present invention includes both a memory and a processor. The memory is capable of maintaining (i) the data structure, which has a plurality of accessible fields, and (ii) a model of at least a portion of at least one process of a plurality of associated processes of the process facility. The model may advantageously include a mathematical representation of at least a portion of the at least one process, defining certain relationships among inputs and outputs of the at least one process. The processor is capable of populating ones of the plurality of accessible fields of the data structure using the model iteratively with a range of possible values of the at least one measurable characteristic. The computer system is capable of using the range of possible values of the at least one measurable characteristic to predict an unforced response associated with the at least one process.
In accordance with an important aspect hereof, the data structure may be populated and maintained on-line (e.g., at a controller, distributed through a process control system, etc.), off-line (e.g., standalone computer, computer network, etc.), or through some suitable combination of the same. Likewise, the data structure may remain static upon population, be dynamic, or be modifiable, at least in part.
Those skilled in the art will understand that xe2x80x9ccontrollersxe2x80x9d may be implemented in hardware, software, or firmware, or some suitable combination of the same, and, in general, that the use of computing systems in control systems for process facilities is known. The phrase xe2x80x9cassociated withxe2x80x9d and derivatives thereof, as used herein, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, be a property of, be bound to or with, have, have a property of, or the like; the term xe2x80x9cincludexe2x80x9d and derivatives thereof, as used herein, are defined broadly, meaning inclusion without limitation; and the term xe2x80x9cor,xe2x80x9d as used herein, means and/or.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.